Thiourea () is an

organosulfur compound Organosulfur chemistry is the study of the properties and synthesis of organosulfur compounds, which are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur der ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

and the

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

. It is structurally similar to

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

(), with the

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

atom replaced by

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

atom (as implied by the ''

thio- The prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry. For example, from the word ''ether,'' referring to an oxy ...

'' prefix). The properties of urea and thiourea differ significantly. Thiourea is a

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. Thioureas are a broad class of compounds with the formula

Structure and bonding

Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å. The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond in

thiobenzophenone Thiobenzophenone is an organosulfur compound with the formula (C6H5)2CS. It is the prototypical thioketone. Unlike other thioketones that tend to dimerize to form rings and polymers, thiobenzophenone is quite stable, although it photoxidizes in ...

, which is 1.63 Å. Thiourea occurs in two

tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...

ic forms, of which the thione form predominates in aqueous solutions. The

equilibrium constant The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...

has been calculated as ''K''_eq is . The

thiol In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

form, which is also known as an isothiourea, can be encountered in substituted compounds such as

isothiouronium In organic chemistry, isothiouronium is a functional group with the formula SC(NH2)2 (R = alkyl, aryl) and is the acid salt of isothiourea. The H centres can also be replaced by alkyl and aryl. Structurally, these cations resemble guanidiniu ...

salts. :

Production

The global annual production of thiourea is around 8,000 tonnes, mostly in China. Thiourea is manufactured by the reaction of

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

with

calcium cyanamide Calcium cyanamide, also known as Calcium carbondiamide, Calcium cyan-2°-amide or Calcium cyanonitride is the inorganic compound with the formula CaCN2. It is the calcium salt of the cyanamide () anion. This chemical is used as fertilizer and is c ...

in the presence of

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. : : :

Applications

Thiox precursor

Thiourea is a precursor to thiourea dioxide, which is achieved using

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

: : Thiourea dioxideis a common reducing agent in textile processing.

Pharmaceuticals

Thiourea has utility in practical heterocyclic chemistry. It is a precursor to sulfathiazoles, tetramisole, and

cephalosporins The cephalosporins (sg. ) are a class of β-lactam antibiotics originally derived from the fungus ''Acremonium'', which was previously known as ''Cephalosporium''. Together with cephamycins, they constitute a subgroup of β-lactam antibiotic ...

Other uses

Other industrial uses of thiourea include production of flame retardant resins, and

vulcanization Vulcanization (British English: vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to ...

accelerators. Thiourea is building blocks to

pyrimidine Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The oth ...

derivatives. Thus, thioureas condense with β-dicarbonyl compounds. The amino group on the thiourea initially condenses with a carbonyl, followed by cyclization and tautomerization. Desulfurization delivers the pyrimidine. The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and

hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...

. Thiourea is used as an auxiliary agent in diazo paper, light-sensitive photocopy paper and almost all other types of copy paper. It is also used to tone silver-gelatin photographic prints (see Sepia Toning). Thiourea is used in the Clifton-Phillips and Beaver bright and semi-bright electroplating processes. It is also used in a solution with tin(II) chloride as an electroless tin plating solution for copper

printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

s. Thiourea has been proposed as a

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

especially under conditions of environmental stress.

Reactions

Thiourea exists in dynamic equilibrium with ammonium thiocyanate at 150 °C. This equilibrium was once exploited as a route to thiourea, but the separation of the mixture is problematic. Thiourea is basic, sustaining protonation at sulfur. According to

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

, the product is , a planar cation. Protonation does not substantially perturb the bond distances.

Oxidation

When treated with a variety of oxidants, thiourea forms a cationic disulfide. Oxidation with

iodine Iodine is a chemical element; it has symbol I and atomic number 53. The heaviest of the stable halogens, it exists at standard conditions as a semi-lustrous, non-metallic solid that melts to form a deep violet liquid at , and boils to a vi ...

proceeds as follows: : Oxidized with hydrogen peroxide gives thiourea dioxide.

Reductant

Thiourea reduces peroxides to the corresponding

diol A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...

s. : Thiourea is also used in the reductive workup of

ozonolysis In organic chemistry, ozonolysis is an organic reaction where the Saturated and unsaturated compounds, unsaturated bonds are Bond cleavage, cleaved with ozone (). Multiple carbon–carbon bond are replaced by carbonyl () groups, such as aldehydes ...

to give

carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

compounds.

Dimethyl sulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula . It is the simplest thioether and has a characteristic disagreeable odor. It is a flammable liquid that boils at . It is a component of the smell produc ...

is also an effective reagent for this reaction, but it is highly volatile (boiling point ) and has an obnoxious odor whereas thiourea is odorless and conveniently non-volatile (reflecting its polarity). :

Precursor to thiols

Thiourea is employed as a source of sulfide, such as for converting

alkyl halide The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents of hydrogen atom. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalka ...

s to thiols. The reaction capitalizes on the

nucleophilicity In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

of the sulfur center and is reminiscent of the protonation of thiourea. S-alkylation gives a

isothiouronium salt In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its vari ...

: : Isothiouronium cations are prone to base hydrolysis to give the thiolate, which can undergo protonation to give the thiol. : : In one example, ethane-1,2-dithiol is prepared from

1,2-dibromoethane 1,2-Dibromoethane, also known as ethylene dibromide (EDB), is an organobromine compound with the chemical formula . Although trace amounts occur naturally in the ocean, where it is probably formed by algae and kelp, substantial amounts are produc ...

: : :

Precursor to metal sulfides

Like other

thioamide A thioamide (rarely, thionamide, but also known as thiourylenes) is a functional group with the general structure , where are any groups (typically organyl groups or hydrogen). Analogous to amides, thioamides exhibit greater multiple bond charact ...

s, thiourea can serve as a source of sulfide upon reaction with metal ions. For example,

mercury sulfide Mercury sulfide, or mercury(II) sulfide is a chemical compound composed of the chemical elements mercury and sulfur. It is represented by the chemical formula HgS. It is virtually insoluble in water. Crystal structure HgS is dimorphic with tw ...

forms when mercuric salts in aqueous solution are treated with thiourea: : These sulfiding reactions have been applied to the synthesis of many metal sulfides..

Precursor to heterocycles

Thiourea is a building block for many heterocycles. It is a precursor to

derivatives via condensation with β-dicarbonyl compounds. : Similarly, aminothiazoles can be synthesized by the reaction of α-halo

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

s and thiourea. : The pharmaceuticals thiobarbituric acid and sulfathiazole are prepared using thiourea. 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is prepared by the reaction of thiourea and

With metals

Being a soft nucleophile, thiourea has an affinity for metal ions, forming

coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

es. Representative is . One practical consequence of its affinity for metals, thiourea is used as a silver polish. Another potential application is the use of thiourea as a lixiviant for gold and silver leaching, bypassing the steps of cyanide use and smelting. Thiourea is a reagent in the Kurnakov test used to differentiate cis- and trans- isomers of certain square planar

platinum Platinum is a chemical element; it has Symbol (chemistry), symbol Pt and atomic number 78. It is a density, dense, malleable, ductility, ductile, highly unreactive, precious metal, precious, silverish-white transition metal. Its name origina ...

complexes. The reaction was discovered in 1893 by Russian chemist Nikolai Kurnakov and is still performed as an assay for compounds of this type.

Safety

The for thiourea is for rats (oral). A

goitrogen Goitrogens are substances that disrupt the production of thyroid hormones. This triggers the pituitary to release thyroid-stimulating hormone (TSH), which then promotes the growth of thyroid tissue, eventually leading to goiter. Goitrogenic dr ...

ic effect (enlargement of the thyroid gland) has been reported for chronic exposure, reflecting the ability of thiourea to interfere with iodide uptake.

References

External links

INCHEM assessment of thiourea
{{Authority control Functional groups